1. Field of the Invention
This invention relates to the synthesis of nonionic polymeric surfactants and their use as adhesion promoter additives in water-based adhesives.
2. Description of the Related Art
Adhesives are conventionally classified into two different types, i.e., (a) solvent-based in which the solid components are dispersed in an organic liquid, and (b) water-based in which the solid components exist as a solid phase dispersed in an aqueous phase. These two different types of adhesives are created by different methods of production.
Solvent-based adhesives can present environmental and safety problems because they contain volatile organic compounds. Volatile organic compounds can cause various problems such as adverse effects on a human organism, safety or hygiene problems inclusive of explosion, fire hazard, etc., and pollution problems inclusive of air pollution.
Further, the use of solvent-based adhesives requires the use of expensive solvent recovery equipment to control emissions of volatile organic compound into the work place or outside environment. For economical and ecological reasons, the industry is trying to replace solvent-based adhesives with water-based adhesive; but, unfortunately, water-based adhesives fail to provide adequate adhesive strength as found in solvent-based adhesives.
The prior art presents several methods of increasing the adhesion of a water-based adhesive.
In conventional processes that use water-based adhesives to bond materials, the materials and adhesive are exposed to heat in order to cause or speed up drying, curing, or setting of the adhesive. A problem with this type of method is that the levels of heat required are typically unsuitable for some materials.
Further, the prior art shows the use of a resin, such as an aqueous solution of a water-soluble polymer, which has been obtained by dispersing a water-dispersible polymer in water, to produce a water-based adhesive. However, in many cases, such a water-based system only using the above water-based resin cannot provide the properties that are required for the adhesives.
The prior art also shows the use of a crosslinking agent in combination with the water-based adhesive for the purpose of improving the adhesion property.
As an example of using a crosslinking agent, there is a system known using a curing agent (or hardening agent) having a free isocyanate group, in combination with a water-based adhesive. However, the system has the limitation that it only has a short work life after mixing the curing agent with the polymer component, and, therefore, this system has a problem in view of the workability or usability thereof.
Recently, the prior art is showing the use of water-based dispersions of either hydroxylated polyurethanes or polyester-urethanes with relatively high molecular weights to produce water-based adhesives. These adhesives offer a stability against oils and greases as well as adhesive strength on the substrates as is required in the shoemaking and furniture industries. However, unfortunately, these types of adhesives do not reach the adhesive strength obtained with solvent-based adhesives.
Adhesive strength is a property very important when working with substrates that are difficult to adhere, such as when attempting to glue elastomeric materials made of poly(ethylene-vinyl acetate) (EVA).
Therefore, it can be appreciated that there exists a continuing need for modifying water-based adhesives to promote the adhesion properties in order to meet the needs of the industry.
A principal object of the invention is the production of a nonionic polymeric surfactant that can be used as an additive in water-based adhesives to increase the adhesion strength.
It is yet another object of the invention to provide a method of producing a nonionic polymeric surfactant that can be used as an additive in water-based adhesives to increase the adhesion strength.
It is yet another object of the present invention to produce an additive for water-based adhesive compositions that can be used for manufacturing footwear or furniture.
In view of the foregoing disadvantages inherent in the known types of water-based adhesives in the prior art, the present inventor discovered a unique additive for a water-based adhesive that will improve the compatibility between the water-based adhesive and the substrate causing in this way a considerable increase in the adhesive strength between the glued surfaces.
Unexpectedly, inventors have discovered a new class of nonionic polymeric surfactants which are particulary useful for promoting the strength of water-based adhesives. Their use in this regard and the method of preparing the instant nonionic polymeric surfactants are also novel.
The present inventor succeeded in synthesizing a novel macroinitiator and synthesizing a novel graft polymer by using such a macroinitiator. The polymeric surfactant, a grafted copolymer, contains aromatic groups in the main chain and acetylethylenimines in the side chains.
Two reactions were required in order to prepare the nonionic polymeric surfactant of the present invention:
1) synthesis of the macroinitiator (MI) through a free-radical polymerization between a monomer and a comonomer.
The free-radical polymerization was initiated by a radical polymerization initiator under nitrogen atmosphere and at a controlled temperature. This reaction formed a linear copolymer called the macroinitiator.
2) grafting a 2-substitute-2-oxazoline with the macroinitiator in the presence of phenyl cyanide under nitrogen atmosphere and a controlled temperature. The reaction was followed by the addition of a solvent and the precipitation of the mixture in diethyl ether. The product obtained was further purified by using a solvent/non-solvent system, followed by vacuum drying until constant weight.
The adhesion promoter of the present invention had the general formula: 
The adhesion promoter included a hydrophobic main chain and hydrophilic side chains. The side chains included at least one poly(2-methyl-2-oxazoline) and poly(2-undecyl-2-oxazoline).
The present invention also concerned a method of preparing the adhesion promotor described above, wherein the method comprised the steps of:
a) preparing a macroinitiator;
b) grafting a 2-substitute-2-oxazoline in the presence of phenyl cyanide with the macroinitiator to produce a mixture, followed by heating the mixture under nitrogen atmosphere, and precipitating the mixture in diethylether to form the polymeric surfactant; and
c) adding the polymeric surfactant to a water-based adhesive to promote adhesion;
wherein the macroinitiator was prepared by a free-radical polymerization between a chloromethylstyrene and methyl methacrylate between 20 to 100xc2x0 C. under nitrogen atmosphere.
Applicants unexpectively found that the above-described polymeric surfactant caused a high increase in the adhesion strength when it was used as additives in water-based adhesives.
The foregoing outlined rather broadly the more pertinent and important features of the present invention in order that the detailed description of the invention that followed may be better understood, and so that the present contribution to the art was more fully appreciated. Additional features of the invention that were described hereinafter form the subject matter of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed were readily utilized as a basis for synthetizing other grafted copolymers for carrying the same purposes of the present invention. It was also realized by those skilled in the art that such equivalent grafted copolymers did not depart from the spirit and scope of the invention as set forth in the appended claims.
Before describing the present invention in detail, it is to be understood that this invention is not limited to the particular monomer structures, polymeric materials, processing conditions, or the like, as such may vary. It is also understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
Many adhesives preferably had a balance of one or more properties such as tackiness at the temperature of use, adhesion, cohesion (shear resistance), elongation, elasticity, color clarity and color stability, and resistance to sunlight and other ultraviolet and degrading radiation sources. Maintaining the requisite balance of such properties, while improving one or more characteristics of such adhesive, was both difficult and unpredictable. Any modification of adhesive compositions, which improved one adhesive property, may detrimentally affect one or more other desirable properties.
The present inventor discovered that polymeric surfactants, grafted copolymers, containing aromatic groups in the main chain and acetylethylenimines in the side chains, could be added to an adhesive to increase the adhesion strength without detrimentally affecting one or more other desirable properties.
Two reactions were required in order to prepare the nonionic polymeric surfactant of the present invention:
1) synthesis of the macroinitiator (MI) through a free-radical polymerization between a monomer and a comonomer. The free-radical polymerization was initiated by a radical polymerization initiator under nitrogen atmosphere and at a controlled temperature. This reaction formed a linear copolymer called the macroinitiator.
2) grafting a 2-substitute-2-oxazoline with the macroinitiator in the presence of phenyl cyanide under nitrogen atmosphere and a controlled temperature. The reaction was followed by the addition of a solvent and the precipitation of the mixture in diethyl ether. The product obtained was further purified by using a solvent system, followed by vacuum drying until constant weight.
Macroinitiator
Typical alkyl methacrylates that could be used as monomers have 1-8 carbon atoms in the alkyl group and are, for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-ethyl hexyl methacrylate, other monomers are acrylonitrile, methacrylonitrile, ethylenically unsaturated monoolefins such as ethylene, propylene and butylene; diolefin such as butadiene, isoprene, vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; vinyl ketones such as vinyl methyl ketone and methyl isopropenyl ketone, pentafluoropropyl methacrylate, pentafluoropropyl acrylate, styrene and derivatives; preferably methyl methacrylate.
As the comonomer copolymerizable with the monomer described above upon preparing the macroinitiator, there could be used together bromomethylstyrene, Iodomethylstyrene, chloromethylstyrene (mixture of meta- and para-isomers in a 70:30 molar ratio) and derivatives preferably, chloromethylstyrene.
Further, the polymerization initiator for use in the polymerization included, for example, known radical polymerization initiators, for example, a usual radical generator such as 2,2-azobisisobutyronitrile, benzoyl peroxide, di-tertiarybutyl peroxide, di-cumylperoxide, tertiaryamyl peroxide, cumenehydroperoxide, di(n-propyl)peroxydicarbonate, peresters such as amyl peroxyacetate and the like; a redox type radical generator such as hydrogen peroxide-iron compound, preferably, benzoyl peroxide.
Although there were no particular restrictions to the polymerization temperature for conducting such polymerization, it was appropriate to conduct the bulk radical polymerization usually at a temperature from 20 to 120xc2x0 C., preferably from 50 to 100xc2x0 C., most preferable 80xc2x0 C.
The most adecuated solvent/non-solvent system for purification of macroinitiator is ethyl acetate/methanol or chloroform/methanol.